The construction of a so called unitized automobile body commences with the formation of individual major panels by stamping the panels from a sheet metal blank. Typically, these major panels include a floor panel, right and left body side panels, a fire wall and either a roof panel or transversely extending header members upon which a roof panel is subsequently mounted. After the individual panels are stamped, some preliminary assembly operations may be performed on the individual panels as, for example, adding door hinge and latch hardware to the body side panels such at appropriate locations on the door opening, adding seat mounting brackets and reinforcements to the floor panel, etc.
A set of panels which are to constitute a subassembly of the finished vehicle body are then brought together and loosely assembled to each other. This initial loose assembly frequently is accomplished by a so-called toy tab arrangement in which one panel is formed with a tab projecting from one edge which is received in a slot of an adjacent panel. This technique interlocks the panels and frame members to each other to form a loosely assembled vehicle body wherein the panels and frame members will not separate from each other, but the panels and frame members may tilt or move relative to one another. The loosely assembled subassembly is then brought to a welding station which welds the various panels and frame members to each other in a rigid, permanently assembled relationship.
This initial welding step is one of the most important steps in the assembly of the vehicle body because it establishes the final assembled alignment of the various panels and headers to each other which is essential to subsequent assembly operations performed on the subassembly. It is thus essential that the various panels and headers be precisely and accurately located relative to one another and held fixedly in the desired positions during the welding operation. The positioning of the various panels and header members during the welding operation is accomplished by clamping frames which carry a plurality of individual clamps arranged to clamp various body components in the desired position.
Because the relative positioning of the various panels and headers is critical, it is desirable to perform as many welding operations as possible within the same welding station since the vehicle body will be relocated and reclamped at subsequent stations along the production line. Due to variations between assembly stations and variation and movement of the various panels and headers, it is almost impossible to relocate and reclamp the vehicle body without stacking up tolerances or creating variances amongst the relative positioning of the various panels and headers. Therefore, it is desirable to frame as much of the vehicle body as possible within the same welding station so that a maximum number of welding operations can be performed on the vehicle body without having to clamp and relocate the vehicle body, which may increase the tolerances between the relative positioning of the various panels and headers of the vehicle body and decrease the repeatability between consecutive vehicle bodies.
To accomplish this task, programmable robotic welders have been utilized to perform several welds at different locations on the vehicle body at one welding station. The programmable robotic welders are typically located at opposite sides of the conveying line at the welding station, and when the vehicle body subassembly is located at the welding station, the head of one welder may, for example, be extended to pass through the door opening to apply several tack welds along the seam between the body side panel and the floor panel. In those cases where the clamping frames are positioned at opposite sides of the vehicle body, clearance problems may restrict motion of the welding head which must pass through the clamping frame before it has access to the vehicle body. This can require that the portions of the vehicle body that could not be accessed by the welding head at a first welding station must be accessed at a subsequent, second welding station. Again, this is an undesirable situation since the vehicle body must be relocated and reclamped at the subsequent, second welding station thereby increasing the amount of tolerances which may occur between the relative positioning of the various panels and headers of the vehicle body and decreasing the amount of repeatability between consecutive vehicle bodies.
Another problem which arises where separate clamping frames are employed at opposite sides of the vehicle body is that the two clamping frames may be independently located in a predetermined relationship relative to each other and to the position occupied by the vehicle body which the frames are to clamp. Since such separate clamping frames are not directly connected to one another, they must utilize a common reference that is either defined by a spacial orientation or via a fixture or linkage assembly. These types of systems exhibit problems with repeatability as such referencing techniques inherently create tolerance build ups within the systems due to repeated movements, thermo expansion and contraction, wear, etc. When such separate clamping frames are changed to accommodate different vehicle body configurations, the problems with repeatability are magnified.
In today's automotive industry, it is common for one particular car model to have several different body styles. This requires different clamping and welding locations as well as access areas in which clamping and welding apparatus may be extended therethrough. To prohibit having to supply separate assembly lines and welding stations for each body style of the particular car model, the welding stations must be able to adapt to a plurality of different body styles in a quick and efficient manner while ensuring the accuracy and repeatability that are required of the welding process.
Programmable robots have been utilized to compensate for the different body styles while others have utilized manual welders to complete the welds that are not common with the other body styles. Obviously, manual welding is an inefficient process, and the programmable robots still require the use of a clamping means to support the vehicle body during the welding process. Some applications have fixedly mounted a clamping means on the end of a programmable robotic arm so that the clamping means can also adapt to a plurality of different body styles, but not all applications are receptive to such a device. Access, cost and efficiency typically favor the clamping means to be independent of the programmable robotic arm. Thus, it would be desirable to have a framing apparatus that adapts to a plurality of different vehicle body styles in an efficient manner.